The present invention relates generally to polycrystalline diamond (PCD) and, more specifically, to method of strengthening PCD compacts.
Polycrystalline diamond (PCD) materials are formed by combining diamond grains with a suitable catalyzing material under high pressure and high temperature conditions. Under such conditions, the catalyzing material promotes diamond-to-diamond bonding between the diamond grains. As a result, a PCD structure is formed. The resulting PCD structure has enhanced wear resistance and hardness characteristics that make the PCD structure useful in oil and gas drilling cutters and other applications. Catalyzing material is any material with the ability to help form bonds between adjacent diamond crystals. Examples of catalyzing material include but are not limited to cobalt, iron, and nickel.
A catalyzing material that is often used in PCD is cobalt. PCD typically comprises from 85% to 95% by volume diamond with catalyzing material, other elements, and void space comprising the remaining volume. The catalyzing material and other elements are found in the voids that exist between the bonded diamond grains. The catalyzing material facilitates diamond-to-diamond bonds between diamond grains in the PCD. Diamond to catalyzing material bonds are also formed under high pressure and high temperature.
As a traditional PCD tool or compact is used in abrasive applications, such as degrading a drilling formation, heat is generated at the working surface of the PCD compact where the PCD compact contacts the drilling formation. Heat causes the catalyzing material and the diamond grains in the PCD compact to expand at a rate consistent with their respective rates of thermal expansion. Often, the coefficient of thermal expansion of the catalyzing material is higher than the coefficient of thermal expansion of the diamond. As a result, the catalyzing material expands at a faster rate than the diamond grains. Consequently, the catalyzing material pushes on the diamond grains as they expand, which puts strain on the diamond-to-diamond bonds. Further, since the catalyzing material can also be bonded to the diamond grains, the catalyzing material also pulls on the diamond grains as they thermally expand, placing additional strain on the diamond-to-diamond bonds. If the strain on the diamond-to-diamond bonds is sufficient enough, the diamond-to-diamond bonds will break, resulting in thermal degradation of the PCD compact particularly when temperature begins to exceed 600° C. at the working surface. Common results of such thermal degradation in a traditional PCD compact include micro-cracks, cracks, chips, fractures, delaminating, and dulling of the cutting edge. Catastrophic breakage of the PCD can also occur.
One technique that has been used to prevent the thermal degradation issues from occurring in the PCD material during such drilling applications is to permanently remove substantially all the catalyzing material from just the volume adjacent the working surface of the PCD material. Thus, as the PCD material's working surface heats up there is no catalyzing material in the PCD material's surface to expand at a different rate than the diamond grains. However, the permanent removal of substantially all the catalyzing material from the volume adjacent the PCD material's working surface creates void space that can weaken the overall toughness and impact resistance of the cutter.